1. Field of the Invention
This invention relates to an optical transmission system, and more particularly to an optical transmission system in which light emitted from a light-emitting element is transmitted through an optical transmission line, and received by a light-receiving element.
2. Description of the Prior Art
In recent years, an optical transmission system has been widely used, for example, between computers, or between printed circuit boards, or even between chips on such boards. However, as the signal processing speed increases, the disadvantages of the electrical transmission system have attracted considerable attention. The disadvantages include signal transfer speed reduction and cross talk, both due to distributed capacity at electrical interconnections. In addition, it has been desired to reduce power consumption (later described in detail) in the optical transmission system.
FIG. 8A shows a schematic configuration of a conventional optical transmission system, and FIG. 8B shows signal waveforms in the system. In FIG. 8A, an input electric signal having a waveform "a" is fed into an input terminal 50 so as to energize a semiconductor light-emitting element 52. The element 52 then emits a light pulse having a waveform "b". The thus obtained light pulse "b" is transmitted to a semiconductor light-receiving element 54 through an optical fiber 53. The element 54 then produces an electric signal having a waveform "c" at an output terminal 56.
As can be seen from FIG. 8B, the input electric pulse signal "a" is converted into the light pulse "b" with substantially no change. This means that the element 52 must be energized so as to emit light during the entire ON time of the input electric pulse signal "a". It would be beneficial for the continuous power consumption to be reduced.